Derek Ellison asks about the ratio of DNAs in stool samples.
I have heard that human stool samples consist of about 50% E. coli
cells (mostly dead). I wouldn't know how to estimate the surviving fraction
of the original DNA, but it seems that rather a lot would be there. Other
DNAs from undigested cells in food might also be there to complicate the
situation even further. The only human DNA I would expect is from sluffed-
off intestinal epithelia. I would guess that the intestinal tract would be
very efficient at absorbing bases and small DNA fragments. How all this con-
tributes to the ratio is hard to predict. Perhaps a CG vs AT ratio would be
useful--especially if the ratio is very different for humans vs E. coli.
Yours,
Bill Tivol